Photolithography process is necessary in manufacturing semiconductor devices, for example, it is necessary for manufacturing the array substrates in Thin Film Transistor Liquid Crystal Display (TFT-LCD) and Active Matrix Organic Light-Emitting Diode (AMOLED). The Photolithography process includes cleaning, photoresist coating, hardening, exposing, developing, wet etching or dry etching, stripping etc.
In the exposure process, when the exposure process is performed by the exposure machine, in order to make the coincidence degree between patterns formed on respective layers of semiconductor using different mask plates satisfy requirements, and meanwhile, in order to assure that the seaming degree between respective scans performed on the same layer using the same mask plate satisfies requirements, accurate alignment must be guaranteed.
In order to increase productivity, a plurality of semiconductor devices are generally formed on a large substrate, wherein the plurality of semiconductor devices are formed through the same photolithography process, then the substrate is divided into a plurality of separate semiconductor devices or unit substrates each having at least two semiconductor devices. For a large-size array substrate, as the size of the substrate is larger than that of the mask plate, and pixel areas are located inside the substrate, therefore, the alignment marks generally are not allowed to be directly provided on the pixel areas, but provided on the periphery of the substrate 1, as shown in FIG. 1.
However, if only the alignment marks at the periphery of the substrate are used in the exposure process, then the alignment marks on the mask plate must not coincide with the alignment marks completely due to limitation of the size of the mask plate, thus the alignment accuracy is decreased largely, and in the exposure process, it is difficult to assure that the seaming degree between patterns in the same layer and the coincidence degree between patterns in respective layers of the semiconductor device satisfy requirements, which leads to high defective rate of resultant substrates.